The present invention relates to a nonwoven having a non-symmetrical bonding configuration yielding low tensile strength and high percent elongation in a first direction (e.g., CD) and high tensile strength and low percent elongation in a second direction (e.g., MD).
Spunbond nonwoven fabrics are made of continuous strands or filaments that are laid down on a moving conveyor belt in a randomized distribution. In a typical spunbond process, resin pellets are processed under heat to a melt and then fed through a spinnerette to create hundreds of thin filaments or threads. Jets of air cause the threads to be elongated, and the threads are then blown onto a moving web where they are laid down and sucked against the web in a random pattern to create a fabric. The fabric then passes through a bonding station. Bonding is necessary because the filaments or threads are not woven together.
The typical bonding station includes a bonding roll defining a series of identical raised points (bonding points). These bonding points are generally equidistant from each other and are in a uniform symmetrical pattern extending in both the machine direction (MD) and the cross direction (CD).
Other nonwoven fabrics include fabrics made from staple fibers, meltblown fibers, carded fibers and short cut fibers. As used herein the terms xe2x80x9cspun fibersxe2x80x9d and xe2x80x9cfibersxe2x80x9d include the spun filaments described above as well as staple fibers, meltblown fibers, carded fibers and short cut fibers.
A non-symmetrical bonding pattern could result in a fabric with an expected or standard elongation in one direction (e.g., MD), but increased elongation in the other direction (e.g., CD). This is a desired attribute in situations where minimal elongation is required in the machine direction and yet high elongation is required in the cross direction. For example, any elongation in the machine direction will disrupt the converting machines that are used to make diapers, while substantial elongation in the cross direction is desired to give each individual diaper some give around the wearer""s waist.
Accordingly, it is an object of the present invention to provide a nonwoven having a non-symmetrical bonding configuration.
Another object of the present invention is to provide a nonwoven fabric which is highly extensible in a first direction (typically the CD) as compared to a second direction (typically the MD).
Another object is to provide such a nonwoven having low tensile strength and high percent elongation in the first direction (typically the CD), and high tensile strength and low percent elongation in the second direction (typically the MD).
It is also an object of the present invention to provide such a nonwoven which is simple and economical to manufacture, use and maintain.
It has now been found that the above and related objects of the present invention are obtained in a nonwoven having high elongation in a first direction (typically the CD) and low elongation in a second direction (typically the MD). The nonwoven has a plurality of bonding points defining a total bonding area along the second direction greater than along the first direction.
In a preferred embodiment, the total bonding area along the second direction is 1.1-5.0 times greater than along the first direction. The nonwoven has unbonded fiber portions and bonded fiber portions, with a bonded portion/unbonded portion ratio greater along the second direction than along the first direction. The first and second directions are mutually transverse, with the first direction preferably being the cross-direction (CD) and the second direction preferably being the machine direction (MD).
Where the bonding points are substantially circular, square or diamond shaped in plan, each of the bonding points are disposed closer to each other in the second direction than in the first direction. The bonding points define gaps of unbonded nonwoven between adjacent bonding points in the first direction of a length 1.1-3.0 times greater than the gaps of unbonded nonwoven between adjacent bonding points in the second direction.
Where the bonding points are substantially oval or rectangular in plan, each of the bonding points is elongated, extends at an angle less than 45 degrees relative to the second direction, and has an extension along the second direction 1.1-10.0 times greater than along the first direction. The bonding points define gaps of unbonded nonwoven between adjacent oval bonding points in the first direction of a length 1.0-3.0 times the length of the gaps of unbonded nonwoven between adjacent bonding points in the second direction.
The nonwoven is defined by substantially randomly oriented fibers, and is preferably a spunbond. The bonding points are produced by using an engraved roll to form bonding points on the nonwoven.